A number of different differential forms have been developed for the practice of differential confocal microscopy. In one differential form, the Nomarski microscope measures one component of a conjugated quadratures of fields corresponding to the electrical interference signal of two images superimposed in an image plane. In another differential form, the conjugated quadratures of a dark field are measured one point at a time. In another differential form, the conjugated quadratures of each of two fields corresponding to two images superimposed in an image plane are measured one point at a time. Commonly owned U.S. patent application Ser. No. 09/917,276 (ZI-16) entitled “Differential Interferometric Scanning Near-Field Confocal Microscopy” by Henry A. Hill, the contents of which are incorporated herein by reference, teaches how to practice differential interferometric scanning near-field confocal microscopy.
But none of these described systems or techniques involve differential interferometric confocal microscopy wherein an array of conjugated quadratures of fields are measured jointly, where the components of each conjugated quadratures may be measured jointly, and where each conjugated quadratures represents a difference of conjugated quadratures of fields of beams scattered/reflected or transmitted by a pair of spots in or on a substrate. Also, none of these systems or techniques involve dark field differential interferometric confocal microscopy wherein an array of conjugated quadratures of fields are measured jointly, where the components of each conjugated quadratures may be measured jointly, where each conjugated quadratures represents a difference of conjugated quadratures of fields of beams scattered/reflected or transmitted by a pair of spots in or on a substrate, and where the nominal values of the conjugated quadratures of the array of conjugated quadratures is zero, i.e., the field that is being measured is nominally dark.